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Section 9.2 Summary – pages 225-230 The chloroplast and pigments To trap the energy in the sun’s light, the thylakoid membranes contain pigments, molecules that absorb specific wavelengths of sunlight. Although a photosystem contains several kinds of pigments, the most common is chlorophyll. Chlorophyll absorbs most wavelengths of light except green.

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Section 9.2 Summary – pages 225-230 Light-Dependent Reactions As sunlight strikes the chlorophyll molecules in a photosystem of the thylakoid membrane, the energy in the light is transferred to electrons. These highly energized, or excited, electrons are passed from chlorophyll to an electron transport chain, a series of proteins embedded in the thylakoid membrane.

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Section 9.2 Summary – pages 225-230 This “lost” energy can be used to form ATP from ADP, or to pump hydrogen ions into the center of the thylakoid disc. Electrons are re-energized in a second photosystem and passed down a second electron transport chain. Light-Dependent Reactions

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Section 9.2 Summary – pages 225-230 The electrons are transferred to the stroma of the chloroplast. To do this, an electron carrier molecule called NADP is used. NADP can combine with two excited electrons and a hydrogen ion (H + ) to become NADPH. NADPH will play an important role in the light- independent reactions. Light-Dependent Reactions

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Section 9.2 Summary – pages 225-230 The oxygen produced by photolysis is released into the air and supplies the oxygen we breathe. The electrons are returned to chlorophyll. The hydrogen ions are pumped into the thylakoid, where they accumulate in high concentration. Restoring electrons

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Light Reactions Takes place on thylakoids Electrons excited from chlorophyll Water is split to donate the electrons. The waste is oxygen. It is released into the air Sunlight is needed to split the water and excite the electrons 2 products go to dark reactions: –1) ATP –2) NADPH (carries electrons and hydrogen) Products goes to Calvin Cycle (Dark reactions) to help make sugar.